Random
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On separation of Zn/C battery contents
I have been doing experiments on Zinc-carbon batteries last few months and tried to recycle as much as it could be done into useful chemical reagents.
First thing is they sometimes have iron casing, which can be thrown away.
After that there is zinc casing which can be washed in dilute acetic acid and then few water washes to remove acid.
Then there are graphite electrodes in the middle which can be useful for electrolysis.
And one of most interesting things is black powder in the battery. Black powder contains mainly MnO2 along with carbon, zinc oxide/hydroxide/chloride
impurities and some NH4Cl electrolyte.
To recover zinc as in carbonate, powder should be washed in water and then filtered, powder should be washed again with water after it remains on the
filter.
After that slightly yellow solution should contain ammonia and zinc compounds. Addition of NaHCO3 will precipitate all zinc ions as carbonate which
can be filtered and looks decently white which could indicate a decent purity for some experiments.
Now there are bicarbonate and ammonia ions left in solution along with Na+ ions, I threw the solution away but if you have many batteries and you need
ammonia salts, solution could be evaporated and then recrystalized to yield ammonia salts.
Back to the washed MnO2 powder, it still contains water insoluble zinc impurities along with a small amount of other metal oxides and hydroxides.
Thoroughly mixing it with excess vinegar (acetic acid 9%) and leaving it overnight should remove a big part of these impurities. Filtrate can be again
reacted with NaHCO3 to yield a smaller amount of zinc carbonate again, but this time less pure.
Now we have MnO2 mixed mainly with carbon particles.
I have been experimenting on reduction of it and have observed a successful reaction with K metabisulfite and 9% acetic acid.
Mixed K metabisulfite and MnO2 doesn't do much but dissolved in dilute acetic acid will exothermically react with very little gas evolution (probably
some SO2) to reduce Mn(IV) to Mn(II).
Mn(II) will get into solution as acetate or sulphate. I would recommend using excess of MnO2 and acetic acid in relation to metabisulfite.
Solution can be filtered to get rid of carbon and excess MnO2, yielding very slightly pinkish or colorless solution. On addition of NaHCO3 manganese
carbonate gets precipitated which on standing becomes light brown in color.
This carbonate could be used in synthesis of other manganese salts. Also one could again prepare decently pure MnO2 from it using bleach but I haven't
yet tried the procedure.
"Clean" MnO2 produced with bleach this way doesn't contain carbon and therefore doesn't interfere with for example permanganate synthesis in liquid
melt.
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blogfast25
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This subject has already been exhausted to death here, see for instance the sticky thread on permanganates.
Of all the methods of reducing the 'MnO2' from batteries with the purpose of separation, I'll add the reduction with oxalic acid solution (which is
oxidised to CO2), which works well.
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Random
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I know my post is nothing new but it is like a summary of my successful experiments. I was really dissapointed to find my MnCO3 contaminated with Zn
for example and this procedure prevents that. Also I never knew that there was truly a significant amount of soluble zinc salts in the black MnO2
powder.
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blogfast25
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Quote: Originally posted by Random  | | I know my post is nothing new but it is like a summary of my successful experiments. I was really dissapointed to find my MnCO3 contaminated with Zn
for example and this procedure prevents that. Also I never knew that there was truly a significant amount of soluble zinc salts in the black MnO2
powder. |
There has to be for the cell to work: MnO2 is reduced to, say MnOx (x < 2), zinc is oxidised. I believe it can be washed out with dilute H2SO4.
A more important contaminant in Mn (II or IV) obtained from batteries is iron. Harder to get rid off too...
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S.C. Wack
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Random, you have my support. Apologies for the sudden urge to hang yourself.
It's most sensible to work with spent batteries, unless one wants the zinc too. IIRC battery grade pyrolusite is only getting scarcer and CMD and EMD
is becoming more common; it should not be surprising to find them in Zn/C batteries these days.
MANGANESE RECOVERING FROM ALKALINE SPENT BATTERIES BY AMMONIUM PEROXODISULFATE
Acta Metallurgica Slovaca, Vol. 19, 2013, No. 3, p. 212-222
www.qip-journal.eu/index.php/ams/article/download/163/179
Spent alkaline and zinc – carbon batteries were collected and dismantled...The acid leaching was performed with 2M H2SO4, at 60 °C and 3
hrs...For each test, 25 mL of spent battery leaching solution was brought to desirable pH and then the volume of 40 % ammonium peroxodisulfate for the
suitable concentration was added, according to the experimental plan. During each test, 1 mL of solution was withdrawn after 15 min, 30 min, 1 h, 2 h
and 3 h to measure the concentration of Mn and Zn by AAS...
...the Mn precipitation was the highest (~ 90 %) and Zn precipitation was the lowest [5%]...Optimal conditions to obtain MnO2 are: 20 % (NH4)2S2O8, pH
6, 3 hours of reaction and 90 °C.
...The statistical analysis shown that ammonium peroxodisulfate concentration and temperature had a great positive significant (> 95 %) influence
on the product obtained (CMD). Highest Mn precipitation (aprox. 90 %) was achieved after 3 h of reaction.
X – ray spectra of the solid samples with the highest amount of Mn have shown that the CMD composition is mainly ammonia manganese oxide
...Electrochemical measurements denoted that CMD obtained at pH 6, 90 °C, 20 % (NH4)2S2O8 and 3 h present high electrochemical activity when the
precipitates are kept at 800 °C for 1 h. The electric capacity of this sample shown a high performance in comparison with the commercial
samples.
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Agricola
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Good work, Random. Why not take some pictures and make a handy write-up of the procedure? Next project could include other kinds of batteries.
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Random
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Blogfast, iron is an impurity here. I'm still working on the method to get rid of it. There is hydroxide trick that makes iron(III) precipitate, when
using excess of Mn hydroxides. I have found my solution contaminated with iron and tried a modified version of this. I precipitated MnCO3 along with
other carbonates. Then left that in air and then added dillute acetic acid so that there was excess of carbonates.
Now I have slightly yellowish pinkish solution floating on top of carbonate excess. I'm not sure if I diluted the solution or if I removed most of the
iron. Solution was rusty brown before IIRC.
SC Wack thats some interesting info even though peroxodisulfate seems like rather expensive reagent to separate Mn. I may be wrong though.
Agricola, thanks, I could do a follow up with pictures if I'll have some time in the future. I also plan on dissasembling NiMH batteries but I still
have to figure out how to do it safely.
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Random
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Alright the method to separate iron seem to work.
Contaminated solution should be reacted with NaHCO3 to precipitate all carbonates. I left them in air few days and they seemed to get oxidized. Acetic
acid should be added to these carbonates in less than stoichiometric amount. Carbonates seem to dissolve very slowly. Leave the solution for a few
days and there should be precipitate of iron hydroxides and oxides mostly at the bottom. Solution will be very slightly yellowish. Decant the solution
and add NaHCO3 again, this time carbonates will be white.
It worked for me.
I'm not sure of mechanism how this works. Anyone care to explain?
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blogfast25
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| Quote: Originally posted by Random | Alright the method to separate iron seem to work.
Contaminated solution should be reacted with NaHCO3 to precipitate all carbonates. I left them in air few days and they seemed to get oxidized. Acetic
acid should be added to these carbonates in less than stoichiometric amount. Carbonates seem to dissolve very slowly. Leave the solution for a few
days and there should be precipitate of iron hydroxides and oxides mostly at the bottom. Solution will be very slightly yellowish. Decant the solution
and add NaHCO3 again, this time carbonates will be white.
It worked for me.
I'm not sure of mechanism how this works. Anyone care to explain? |
Yours is a variant. The original has been posted by me here (somewhere) and it works like this.
Set apart about 1/4 of the mixture of Fe(III) and Mn(II) and neutralise it with ammonia to precipitate the mixed hydroxides Fe(OH)3 and Mn(OH)2. Wash
this precipitate carefully to remove all ammonium salts.
Now add the washed filter cake to the three quarters of the original mixture of Fe(III) and Mn(II) and leave it to stand overnight, perhaps stirring
once in a while. The next day all iron will be found in the precipitate and all Mn(II) in the supernatant liquid, which is then filtered off.
Chemically it works like this. When you add the washed mixed hydroxides, they neutralise any acidity in the 3/4 of mixture of Fe(III) and Mn(II), in
such a way that all Fe(III) precipitates because the solubility product (Ksp) of Fe(OH)3 is insanely low. The Ksp of Mn(OH)2 however is much larger
and as a result the Mn(II) does not precipitate.
Another variant is to very slowly and carefully adjust the pH of the Fe(III)/Mn(II) mixture with weak ammonia. At pH 4 - 5 Fe(OH)3 cannot stay in
solution anymore, because of its low Ksp. But at that pH Mn(II) doesn't precipitate yet. Ergo: separation.
It's quite similar to the wet separation of Cu(II) and Zn(II), based on the solubility products of CuS and ZnS. Careful control of pH allows to
precipitate CuS (with H2S) but not the Zn(II).
[Edited on 4-11-2013 by blogfast25]
[Edited on 4-11-2013 by blogfast25]
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Random
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Thanks for the explanation blogfast. Next topic on batteries will be NiMH battery contents separation.
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